Piezoresistive miniature pressure transducer

ABSTRACT

A miniature pressure transducer has an edge-supported flexible diaphragm with a semiconductor chip providing a bridge arrangement of the piezoresistive strain gauge areas bonded to its inner surface to position active tension gage areas at the center of the diaphragm and active compression gage areas at the periphery. The chip is also bonded along its outer periphery to the annular inner surface of the transducer body supporting the edges of the diaphragm to prevent slippage during deflection of the diaphragm, thus placing the effective compression gage areas of the chip outside of the neutral circle within the compression zone on the diaphragm.

United States Patent Inventor James E. Frassrand Arcadia, Calif.

Appl. No. 31,258

Filed Apr. 23, 1970 Patented Nov. 30, 1971 Assignee DynasciencesCorporation Los Angeles, Calif.

PIEZORESISTIVE MINIATURE PRESSURE TRANSDUCER 9 Claims, 5 Drawing Figs.

U.S. Cl 73/398 AR, 73/406, 338/4 Int. Cl G0ll 9/04 Field at Search73/398 AR,

Primary Examiner-Donald O. Woodiel Attorney- Donald E. Nist ABSTRACT: Aminiature pressure transducer has an edgesupported flexible diaphragmwith a semiconductor chip providing a bridge arrangement of thepiezoresistive strain gauge areas bonded to its inner surface toposition active tension gage areas at the center of the diaphragm andactive compression gage areas at the periphery. The chip is also bondedalong its outer periphery to the annular inner surface of the transducerbody supporting the edges of the diaphragm to prevent slippage duringdeflection of the diaphragm, thus placing the effective compression gageareas of the chip outside of the neutral circle within the compressionzone on the diaphragm.

PIEZORESISTIVE MINIATURE PRESSURE TRANSDUCER BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates topiezoresistive strain gauges employing semiconductive chips bonded to anedge-supported diaphragm for operation as a pressure transducer or thelike.

2. Background of the Invention Static and dynamic forces, particularlyfluid pressures, are commonly measured using transducers with anedge-supported flexible diaphragm that deflects convexly or concavely inresponse to force differentials on its opposite faces. As the diaphragmis bowed inwardly, as by an increase in external pressure forces. atension force is produced at the center of the interior diaphragm faceand a compression force results near the edge. Piezoresistive straingauges placed to measure these tension and compression forces on thediaphragm can thus be used to measure the diaphragm deflections as afunction of these surface strains.

Preferably, piezoresistive strain gauge elements are bonded to theinterior diaphragm surface to measure these strains. To maximize signalamplitude, the piezoresistive strain gauge elements are bonded to thediaphragm surface both near the center to measure tension stresses andnear the periphery to measure compression, and are connected in anelectrical bridge arrangement to produce an output signal with a highsignal to noise ratio.

However, with conventional edge-supported diaphragms, the annular areaof compressive stress extends only a short distance inwardly from thesupporting edge. A circular neutral zone is located between thecompression and tension areas only approximately one-third of the radialdistance inwardly from the supporting edge, and maximum compressivestrains occur very near the supporting edge. Therefore, with straingauge bridge arrangements, although the tension gauges are easilydisposed in the area of maximum stress near the center, considerabledifficulty is encountered in placing the compressiori gauges closeenough to the diaphragm edge to obtain suitable response.

With larger transducers, several approaches have been employed in thesolution of this problem. In one such arrangement, as shown in U.S. Pat.No. 3,358,511 issued to D. W. Bargen on Dec. 19, 1967, the diaphragm isformed integral with the transducer body to have a thicker outer edgetapering to a thin center area which has the effect of transferring themaximum compression and neutral zones radially inward towards thediaphragm center so that the compression gauges can be located whollywithin the outer compression area for maximum response. With anotherapproach wherein a separate diaphragm is edge supported by thetransducer body, the interior surface of the tubular transducer body isnotched inwardly at the end supporting the diaphragm to allow placementof the compression gauges on the far outer edge of the diaphragm withinthe notch, thus avoiding the neutral zone, as shown and described inU.S. Pat. No. 3,473,375 to E. E. Jenkins issued Oct. 2l, 1969. A thirdapproach, as shown both in the last-mentioned patent and more fully inthe U.S. Pat. No. 3,434,090 to H. Chelner issued Mar. 18, 1969, thecompression gauge is formed in the shape of a U or M to reduce theradial extent of the required active gauge area at the edge of thediaphragm. In the last-mentioned patent, this feature is combined withthe integral tapered diaphragm type of structure and certain otherfeatures to yield the desired measurement of the compressive strain.

Another development in this field has been the use of planarsemiconductor difiusion techniques for forming the two compressive andtwo tension gauges with Wheatstone bridge connections integrated withina single semiconductive chip. The single chip can then be bonded to theinterior of the diaphragm with input and output connections being madeto contact areas at the ends of the active gauge portions. This has madepossible very much smaller and more reliable transducer elements havingoverall diameters of less than 0.10 inches. With such small sizes,considerable difficulty has been encountered in maintaining a strongrepeatable output signal with the relative decrease in the tension andcompressive areas on the smaller diaphragm. The effective length of thestrain gauges cannot be decreased much below 0.0l0 inches to produce aneffective output level, and even then the compressive gauges shouldoperate efficiently in measuring compressive strain to contribute asmuch as possible to the total output from the Wheatstone bridge.

However, with such small dimensions, the problem of compressive gaugeplacement is greatly magnified, while at the same time the approachesemployed in solving this problem in the prior art also becomeincreasingly impractical, if not impossible. F or example, the walls ofthe transducer body would already be extremely thin so that littleadditional area would be gained by notching. Very precise and costlymachining methods would have to be used to provide uniform tapereddiaphragms to transfer compression area inwardly. Use of an M ormultiple zigzag configurations to reduce the radial extent of thecompression gauge would require extremely precise control of thediffusion techniques to prevent overlapping and shorting of the activeand contact areas.

As a consequence, in most cases where such small strain gauges wererequired, the compression gauges actually detracted from the outputsignal produced by the tension gauges and served only as a dynamicthermal balance in the bridge. Moreover, with the single-chipconstruction of the gauge bridge, the chip is bonded to the diaphragmwith a cementing agent which became subject to slippage in the highstress corner areas in the immediate vicinity of the inner supportingedge of transducer body. This had the effect of reducing output and alsodeveloping a negative hysteresis-type response for static loadings onthe transducer.

SUMMARY OF THE INVENTION The aforementioned difficulties of the priorart, particularly in producing miniature transducer elements, areovercome in a relatively simple inexpensive manner by use of a laminatedstructure in which the periphery of a flat semiconductive chip on whichcompressive gauge areas are formed is not only bonded to the innerdiaphragm surface on one side but also bonded on its other side to theedge-supporting annular end surface of the tubular transducer body. Inthe preferred form, a unitary four-element silicon chip has a flatconfiguration with active piezoresistive areas extending between contactareas produced-by planar diffusion techniques. The active areas formingthe tension gauges constitute parallel strips near the center of thechip, while the compression gauges, preferably U-shaped are defined nearthe periphery of the chip at opposite ends of the tension gauge areas.The chip is bonded by suitable cement to the inner surface of thediaphragm. In the preferred embodiment, the diaphragm consists of acup-shaped member having a tubular sleeve portion that is bonded to theouter surface of a tubular shaft forming the body of the transducer. Thebottom portion of the cupshaped diaphragm member provides a thin flatwall that is flexible in the central circular area overlying the hollowbore of the tubular transducer body to act as a diaphragm. The siliconchip with the piezoresistive active gauge areas and contact areas at onesurface, has its opposite surface bonded to the diaphragm surface in theconventional manner, but with the outer periphery of the chip adjacentthe compression gauge areas extending beyond the diameter of theinternal bore in the tubular transducer body. The cement or bondingagent is applied to the annular end surface of the tubular transducerbody at least in the area of the chip so that its outer peripheryadjacent the compressive gauge is also bonded on its inner surface tothe end surface of the transducer body. This additional bonding on theopposite side of the chip has the effect of extending the compressionarea on the diaphragm inwardly to insure that the active areas for thecompression gauges lie on the outside of the neutral zone to generatemaximum useful signal and of preventing slippage between the chip endsand the diaphragm in areas of high compressive strain. This results in atransducer response having increased linearity and repeatability withoptimum output from the bridge arrangement to improve the signal tonoise ratio.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a slightly enlargedperspective showing the miniature pressure transducer in accordance withthe invention;

FIG. 2 is an enlarged cross-sectional side view of the miniaturepressure transducer of FIG. 1 illustrating the internal connection ofthe lead wires;

FIG. 3 is a greatly enlarged cross-sectional side view of the tip of theimproved pressure transducer of FIGS. 1 and 2 showing the mountingdetails;

FIG. 4 is a partial top cross-sectional view of the improved pressuretransducer of FIGS. 1-3 taken on the line 4-4 through the interior ofone preferred form of silicon chip strain gauge bridge arrangement; and,

FIG. 5 is a schematic circuit diagram showing the equivalent bridgecircuit arrangement involved in the operation of the pressure transducerin accordance with the invention.

DETAILED DESCRIPTION Referring now to FIG. 1, an improved miniaturestrain gauge pressure transducer in accordance with the invention has acylindrical body with active tip portion 11 at one end joined to asmaller diameter terminal extension 12 at the other end. A flat circularend surface 13 provides an active diaphragm area at its center to becontacted by the fluid or other medium in which pressure phenomena is tobe measured. Individual lead wires 14 extend outward from the end of theterminal extension 12 to be connected to appropriate external electricalinput and output circuitry.

Referring now to FIG. 2, a cylindrical transducer body structure 15 hasa hollow cylindrical shape with a large internal bore 17 defined in theactive tip portion 11 communicating with a coaxial smaller diameterinternal bore 19 extending through the terminal extension 12. Athin-walled cup-shaped closure member 21, preferably cast of nickelalloy, fits over the ;.end of the active tip portion 11. The thincylindrical sidewalls of the cup-shaped closure member 21 slidably fitover the end portion of the transducer body 15 which has a slightlyreduced outer diameter. As more fully described, in connection with FIG.3, the annular surface at the tip of the transducer body 15 supports theinner surface of the thin bottom wall of the cup-shaped closure member21 giving edge support around a circular active diaphragm area that lieswithin the region of the enlarged cylindrical bore 17. As explained inmore detail hereinafter, the semiconductive strain gauge elements areaffixed to the inner gauge-supporting surface of the cup-shaped closuremember 21 with contact leads 23 extending into the enlarged bore 17 forconnection to an appropriate interior conductor arrangement.

In the preferred embodiment, the interior conductor arrangement consistsof a five-conductor cable having five mutually insulated small-gaugecable wires 14 that extend through the smaller diameter bore 19 from thecylindrical space within the larger bore 17 to the end of the terminalsection 12. The cable wires 14 within the cable are held in place andthe reduced diameter bore 19 is sealed by epoxy cement that fills theentire cavity. The end of the cable 23 protrudes from the smaller bore19 into the larger bore 17 passing through a circular opening theannular section of an L-shaped cylindrical insulator bracket 25 that isinserted into the large diameter bore 17 to be held in place against theinterior shoulder formed at the junction of the larger and smallerdiameter bores 17 and 19, respectively. The individual wires 13 emergingfrom the end of the cable have the covering insu lation stripped backfrom the ends to expose the metal conductor for solder connection to oneof the strain gauge leads.

The ends of the stripped cable wire 14 are affixed as by an epoxy cementalong the elongated cylindrical portion of the L- bracket and spacedfrom one another for easy connection to the strain gauge leads.

In constructing the transducer, the conductor cable is pushed throughthe smaller diameter bore 19 and through the larger diameter bore 17 toemerge from the end of the active tip region 11. Then the cable end isinserted through circular opening in the L-bracket and the individualwires 14 are separated and the insulation stripped from the ends to bepositioned along the elongated cylindrical portion of the L- bracket 25.The individual small-gauge wire leads from the strain gauge are thensoldered in place on the appropriate exposed ends of the individualwires 14 with care being taken to maintain proper spacing between them.The cable is then pulled back into position with the annular end sectionof the L-bracket 25 against the internal shoulder, to which it ispreferably affixed by cement, while the cup-shaped enclosure member 21,to which the gauges are attached as hereinafter described, is moved intoposition over the end of the active tip portion 11 of the transducerbody structure 15.

As shown in more detail in the enlarged illustration of FIG. 3, asemiconductive strain gauge arrangement is initially bonded to theinterior bottom surface of the cup-shaped closure member 21. In thepreferred embodiment, the semiconductive strain gauge bridgearrangement, instead of constituting separate semiconductive chipsbonded in the active diaphragm region, consists of a single monolithicsemiconductive chip 27 containing active strain gauge areas definedbetween intermediate contact areas, as more particularly described withrelation to FIG. 4. Metallic contacts 29 are plated or otherwise formed,as by use of an evaporation technique with etching, to cover the contactareas. A very small gauge lead wire 31, preferably of gold, has its endalloyed or soldered to the metal contact 29 with its other end solderedor otherwise connected to the exposed end of a respective one of thecable wires 14.

The entire surface of the chip 27 opposite the contacts 19 is coatedwith a uniform layer 32 of an appropriate adhesive material, such as anepoxy, phenolic or ceramic cement, that forms an extremely strong bondbetween the surface of the chip 27 and the adjacent interior bottomsurface of the metal sheet material forming the cup-shaped closuremember 21. As shown in FIG. 3, the end of the tip portion 11 of thetransducer body preferably is formed with an annular shoulder 33 havingan inner annular raised contact surface 35 providing the edge supportfor the active diaphragm area defined in the circular center portion ofthe thin bottom of the cup-shaped closure member 21. To prevent shortingof the gold contact leads 30 against the metal body structure 15, theinterior surface of the large diameter bore 17 may be coated with a thinlayer 37 of an appropriate insulating material such as a varnish orplastic. Before the end of the active tip portion 11 of the transducerbody is inserted to be received within the sidewalls of the cup-shapedclosure member 21, an appropriate adhesive 39, preferably of the sametype forming the adhesive layer 31, is applied along the outertransducer body surfaces in the area of slightly reduced diameter, andalso, or instead, to the adjacent interior sidewall surfaces of thecup-shaped closure member 21 to form a rigid seal. At the same time, auniform adhesive layer 41 is applied either to the interior surface ofthe chip 27 in the areas overlapping the annular edge support 35 at thevery end of the transducer body, or may also, or instead, be applied tothe adjacent corresponding areas on the raised edge support surface 35,to form a strong bond between the transducer body and the oppositeoverlapping ends of the silicon chip 27. This results in a bondedlaminated construction in the areas of over lap with the silicon chip inthese areas being fixedly attached both to the transducer body and thebottom of the cup-shaped enclosure member 21.

Referring now to FIG. 4, in the preferred form of this inven tion, thesilicon chip 27 may be of the type illustrated, in which elongated.narrow active gauge areas 43 and 45, respectively, are formed inappropriate locations on a single chip to constitute the tension andcompression gauges. The tension gauge areas 43 consist of two narrowstrips parallel to one another on either side of the center of theactive diaphragm. The tension gauge areas 43' are each separated fromcompression gauge areas 45 by inactive contact areas 47, 48, 49, 50 and51, which provide low-impedance contact between the adjacent activegauge areas. The chip 27 has an overall elongated, approximatelyrectangular shape with reduced width portions at either end. Eachcompression gauge has a U- shaped configuration consisting of two shortactive gauge area strips 45 jointed by a short, low-resistance crosscontact area 53. This provides an active length disposed in anapproximate radial direction which is effectively equal to the sum ofthe lengths of the two active gauge area strips 45.

Referring now to FIG. 5, a schematic circuit diagram illus trates thebridge arrangement provided by the single silicon chip arrangement. Theopen connection between the contacts 50 and 51 provides a five-terminalbridge arrangement which permits incorporation of compensation circuitryfor balancing the slight impedance discrepancies in the different legsof the bridge. A DC input excitation is supplied from a source 55, suchas a battery or constant current source, through three of the wire leads31 to the metal contacts 29 overlying the contact areas 48, 50 and 51,and the output from the bridge is supplied to an output circuit 57 fromthe metal contacts 29 overlying the contact areas 47 and 49 along theother two wire leads 31. Both the excitation source 55 and the outputcircuit 57 in practice are coupled from remote locations by the cablewires 13.

A desired chip configuration as shown in FIG. 4, may best be achieved byuse of well-known planar techniques commonly employed in the productionof integrated circuits. The particular types of chips to be employed inthe preferred embodiment of this invention are the types sold undertrade designations SP-4 and SP-24 previously by Whittaker Corporation,and presently by the assignee of the present inven-. tion. Suchintegrated strain gauge transducer chips containing a five-terminalbridge arrangement have been commercially available for some time sothat the complete details of their manufacture may not be consideredherein. Briefly, the concept involved is one of utilizing a unitarysemiconductor single crystal having adjacent zones of differentconductivity types so that a high-impedance barrier is formed by arectifying junction between zones of different conductivity type, thuselectrically isolating adjacent zones without necessity of structural orthermal separation. The chip 27 preferably consists of a unitarysingle-crystal body of semiconductor material produced conventionally,as by growing a single-crystal silicon structure from a small seedcrystal withdrawn from a silicon melt. in this example, the crystal isof N-type conductivity produced by introducing an N-type doping agentsuch as arsenic into the molten silicon. Thin wafers are sliced from thecrystal body and lapped to an appropriate thickness, for example about0.014 inch, and aligned with longitudinal and lateral dimensionsextending in a desired crystallographical direction. An initial etchingoperation, commonly using an etching solution with equal parts ofhydrofluoric, hydrochloric and acetic acids, is used to reduce thethickness of the wafer to remove any remaining surface damage caused bythe lapping operations. With the planar diffusion technique, theresulting wafer is then oxidized at high temperature with or withoutsteam to form a silicon dioxide layer 59 that insulates and protects theentire outer surface of the wafer. Using well-known photoresistive orother suitable techniques, grooves are etched in one surface of thewafer to define the shape of the individual chips 27. These area arethen reoxidized to form a protective silicon dioxide coating.

In forming the active gauge and contact areas, a mask is carefullypositioned over one of the flat surfaces of the wafer to which thephotoresistive layer is applied. The mask is shaped to expose only thosesurfaces within each chip area surrounding the active gauge and contactareas. The unactivated photoresistive material is removed to uncover theactive gauge and contact areas permitting a suitable oxide etchingsolution, such as hydrofluoric acid, to be applied to remove the silicondioxide layer down to the surface of the crystal. The remaining etchingsolution is then removed by washing or application of a buffer solution,and the wafer thus prepared is placed in a diffusion furnace containinga P-type dopant, such as boron, which is ten diffused into the exposedcrystal surfaces to a depth of approximately 0.00025 inch, commonly thedesired depth for producing the narrow piezoresistive active gaugeareas. This results in the relatively lightly doped P-type region on allof the exposed crystal surface areas.

The crystal is then reoxidized and covered with photoresistive materialto cover the previously exposed areas now doped to form P-type regions.Then another mask outlining the contact areas 47, 48, 49, 50, 51 and 53on each chip is carefully positioned on the wafer with the etch beingapplied to the resulting exposed areas to remove the most recentlyapplied silicon dioxide layer. After the protective silicon dioxidelayer is removed in the desired areas, the chip is again placed into ahigh-temperature diffusion furnace, this time containing a much higherconcentration of P-type dopant, such as boron, to increase the P-typeimpurity level in the contact areas to produce what is commonly known asP+ region. The P+ regions provide an extremely low resistance pathbetween the adjacent P-type regions. Again, a protective silicon dioxidelayer is formed over the entire wafer, and another mask is positioned touncover the areas at the center of the P+ contact areas 47, 48, 49, 50and 51, this time to permit evaporative deposition of the metal contacts29. The heavily doped P+ region in contact with the evaporated metalcontact 29, which may for example be aluminum, provides a low-resistanceohmic connection of the leads 30 to the ends of the bridge elementsdefined on each chip.

Upon completing the evaporation of the contacts 47, 48, 49, 50 and 51 oneach of the chip areas of the wafer, an oxide removing etch is appliedto the entire opposite surface of the wafer to remove the protectivesilicon dioxide layer. Further etching of this surface removes thethickness of the silicon wafer to meet the bottom of the groovespreviously etched to define the individual chip areas, thus separatingthe wafer into individual chips 27. The thin-gauge wire leads 31,preferably of gold, can then be soldered into place, or preferablynailhead" bonded by thermocompression bonding, on the metallic contactsdeposited at the center of the contact areas.

Of course, the particular chip configuration and its method ofmanufacture may be varied in accordance with the particular gaugeparameters desired, and single-chip bridge arrangements such as employedin the preferred embodiment may be manufactured using other well-knownsemiconductor fabrication techniques, particularly those employed in theintegrated circuit field. Alternatively individual piezoresistive chipsfor each gauge may be employed in accordance with the invention byindividually cementing them in place in the desired locations on thediagram with the compressive gauges being cemented between the raisededge-supporting surface of the transducer body to provide the laminatedsandwich construction for preventing slippage and locating the activegauge areas in the region of maximum strain outside the neutral circle63, as shown in FIG. 4.

This laminated construction provides a firm, well-defined and staticcompression zone with a relatively simple diaphragm construction. Thecompression zone outside of the neutral circle 63 is extended radiallyinward further than with the simple edge supported diaphragm so that theactive compression gauge areas 45-lie totally within the compressionzone in the approximate location in the area of maximum compressivestrain. in this way, the compressive gauge portions of the bridgearrangement made a substantial positive contribution to the total bridgeoutput, typically at least 60 percent of the output that would beproduced by the tension gauges alone. With the conventionaledge-supported diaphragm pressure transducer using the same or a similartype chip, the compressive strain region might vary due to slippagecaused by the end portions of the chip becoming unbonded from thediaphragm and the active compression gauge areas were typically locatedvery close to or even intersected by the neutral circle so that theoutput contribution was either very small or actually detracted from thetotal output, when as frequently occurred, the compressive gauge areaswere actually subjected to more tension strain than compressive strain.As a result, the pressure transducers in accordance with this invention,provide output signals with superior linearity, greatly reducedhysteresis, and substantial repeatability to maintain the gauge outputand accurate measure of the pressure phenomenon being measured. Inaddition, the additional bonding on both sides of the silicon chip 27results in overall strengthening to the entire mechanical structure,especially in providing increased mechanical support for the delicatesilicon chip. The unique features of this invention provide a veryaccurate pressure transducer of extremely small size that is most usefulin making point measurements in wind tunnel tests using miniature modelsof an aerodynamic shape. These transducers are also particularly usefulbecause of their microminiature dimensions for use in biomedicalapplications, such as the measurements of blood pressure at specificpoints in the circulatory system by inserting the transducer through useof an appropriate catheter device into a vein or artery.

What is claimed is:

1. An improved pressure transducer comprising: an elongated hollowtransducer body having an internal bore coaxial with the axis ofelongation of the body and a flat supporting end surface surrounding theopening at the end of said bore;

an end closure member having a thin flexible flat wall extending acrosssaid end surface to cover the open end of said bore, said end closuremember being bonded to said transducer body with opposing edgessupported by said end surface to provide a central active diaphragm areacorresponding to the dimensions of said bore;

flat semiconductor means having active piezoresistive strain gauge areasdefined therein bonded to the inner surface of said thin flexible wallwith a pair of elongated tension gauge areas disposed parallel to oneanother adjacent to center of said diaphragm area and a pair ofcompression gauge areas being disposed partially within said activegauge area with a portion extending outwardly past said active diaphragmarea between said end surface and the inner surface of said flat wall;and,

adhesive means bonding said compression and tension gauge areas of saidchip means to the inner surface of said flat wall and fixedly bondingsaid outwardly extending portion of said semiconductor means containingsaid compression gauge areas to said end surface to prevent slippage.

2. The improved pressure transducer in claim 1 wherein:

said internal bore is cylindrical in shape, said flat supporting endsurface is annular in shape surrounding said cylindrical internal bore,and said flat wall is disc-shaped to cover said annular end surface andthe end of said bore to define a circular active diaphragm areacorresponding to the inner dimensions of said bore.

3. The improved pressure transducer of claim 1 wherein:

said semiconductor means comprises a single elongated silicon chip withactive compression and tension gauge areas defined thereon in a bridgearrangement with intermediate contact areas, said compressive gaugeareas each consisting of a U-shaped compressive gauge element formed atthe opposite ends of said chip with the outer ex tremities of saidU-shaped areas being bonded by said adhesive means to the abuttingportions of said supporting end surface.

4. The improved pressure transducer of claim 1 wherein:

said end closure means comprises a cup-shaped metal member with a bottomwall defining said flat thin wall containing said active diaphragm areaand with sidewalls being bonded to the outer surfaces of said transducerbody.

5. An improved pressure transducer comprising:

diaphragm means having a thin flexible planar portion having 'an activediaphragm area, said diaphragm means having an outer pressure-receivingsurface and an inner gauge-supporting surface;

flat compression strain gauge means bonded to said inner surface at theperiphery of said active diaphragm area with an outer edge portionextending outward past the periphery of said active diaphragm area; and,

a body portion with edge support means having a flat end surface withthe outer portion of said compression strain gauge means being fixedlybonded on opposite sides both to said inner gauge-supporting surface andto said flat end surface.

6. The improved pressure transducer of claim 5 further comprising: I

tension strain gauge means bonded to said inner gauge-supporting surfaceadjacent the center of said active diaphragm area; and,

circuit means electrically connecting said tension and compressionstrain gauge means to produce mutually complementary output signals inresponse to a deflection of said diaphragm means within said activediaphragm area.

7. The improved pressure transducer of claim 6 wherein:

said compression and tension strain gauge means constitute differentnarrow piezoresistive strips defined on a single flat semiconductivechip, said flat compression strain gauge means consisting of twopiezoresistive active areas near the periphery of said chip and saidtension strain gauge means constituting a pair of elongated parallelpiezoresistive active areas adjacent the center of said active diaphragmarea at the center of said chip; and,

said connection means comprises low-resistance contact areas definedwithin said chip between the ends of said elongated piezoresistiveactive areas and the adjacent ends of said piezoresistive active areasconstituting said compression strain gauge means.

8. The improved pressure transducer of claim 7 wherein:

each of said piezoresistive active areas constituting said compressionstrain gauge means comprise narrow piezoresistive strips parallel to oneanother and connected in series by additional low-resistance contactareas.

9. The improved pressure transducer of claim 8 wherein:

said flat end surface is bonded to the periphery of said chip at theouter extent of said piezoresistive strain gauge areas constituting saidcompression strain gauge mean so that said strain gauge means is locatedwithin said active diaphragm area outside a neutral circle definedbetween compression and tension areas resulting from concave deflectionof said diaphragm.

1. An improved pressure transducer comprising: an elOngated hollowtransducer body having an internal bore coaxial with the axis ofelongation of the body and a flat supporting end surface surrounding theopening at the end of said bore; an end closure member having a thinflexible flat wall extending across said end surface to cover the openend of said bore, said end closure member being bonded to saidtransducer body with opposing edges supported by said end surface toprovide a central active diaphragm area corresponding to the dimensionsof said bore; flat semiconductor means having active piezoresistivestrain gauge areas defined therein bonded to the inner surface of saidthin flexible wall with a pair of elongated tension gauge areas disposedparallel to one another adjacent to center of said diaphragm area and apair of compression gauge areas being disposed partially within saidactive gauge area with a portion extending outwardly past said activediaphragm area between said end surface and the inner surface of saidflat wall; and, adhesive means bonding said compression and tensiongauge areas of said chip means to the inner surface of said flat walland fixedly bonding said outwardly extending portion of saidsemiconductor means containing said compression gauge areas to said endsurface to prevent slippage.
 2. The improved pressure transducer inclaim 1 wherein: said internal bore is cylindrical in shape, said flatsupporting end surface is annular in shape surrounding said cylindricalinternal bore, and said flat wall is disc-shaped to cover said annularend surface and the end of said bore to define a circular activediaphragm area corresponding to the inner dimensions of said bore. 3.The improved pressure transducer of claim 1 wherein: said semiconductormeans comprises a single elongated silicon chip with active compressionand tension gauge areas defined thereon in a bridge arrangement withintermediate contact areas, said compressive gauge areas each consistingof a U-shaped compressive gauge element formed at the opposite ends ofsaid chip with the outer extremities of said U-shaped areas being bondedby said adhesive means to the abutting portions of said supporting endsurface.
 4. The improved pressure transducer of claim 1 wherein: saidend closure means comprises a cup-shaped metal member with a bottom walldefining said flat thin wall containing said active diaphragm area andwith sidewalls being bonded to the outer surfaces of said transducerbody.
 5. An improved pressure transducer comprising: diaphragm meanshaving a thin flexible planar portion having an active diaphragm area,said diaphragm means having an outer pressure-receiving surface and aninner gauge-supporting surface; flat compression strain gauge meansbonded to said inner surface at the periphery of said active diaphragmarea with an outer edge portion extending outward past the periphery ofsaid active diaphragm area; and, a body portion with edge support meanshaving a flat end surface with the outer portion of said compressionstrain gauge means being fixedly bonded on opposite sides both to saidinner gauge-supporting surface and to said flat end surface.
 6. Theimproved pressure transducer of claim 5 further comprising: tensionstrain gauge means bonded to said inner gauge-supporting surfaceadjacent the center of said active diaphragm area; and, circuit meanselectrically connecting said tension and compression strain gauge meansto produce mutually complementary output signals in response to adeflection of said diaphragm means within said active diaphragm area. 7.The improved pressure transducer of claim 6 wherein: said compressionand tension strain gauge means constitute different narrowpiezoresistive strips defined on a single flat semiconductive chip, saidflat compression strain gauge means consisting of two piezoresistiveactive areas near the periphery of said chip and said tension straingauge means constituting a pair of elongated paraLlel piezoresistiveactive areas adjacent the center of said active diaphragm area at thecenter of said chip; and, said connection means comprises low-resistancecontact areas defined within said chip between the ends of saidelongated piezoresistive active areas and the adjacent ends of saidpiezoresistive active areas constituting said compression strain gaugemeans.
 8. The improved pressure transducer of claim 7 wherein: each ofsaid piezoresistive active areas constituting said compression straingauge means comprise narrow piezoresistive strips parallel to oneanother and connected in series by additional low-resistance contactareas.
 9. The improved pressure transducer of claim 8 wherein: said flatend surface is bonded to the periphery of said chip at the outer extentof said piezoresistive strain gauge areas constituting said compressionstrain gauge mean so that said strain gauge mean is located within saidactive diaphragm area outside a neutral circle defined betweencompression and tension areas resulting from concave deflection of saiddiaphragm.